ModWorker addresses ModPrefork’s performance problem by using threads to serve large numbers or requests with fewer system resources. To enable ModWorker in CentOS, edit the file /etc/sysconfig/httpd and uncomment the line HTTPD=/usr/sbin/httpd.worker. Then restart Apache with service httpd restart. To verify in what mode Apache is running use the command apachectl -l to list all of Apache’s loaded modules and look for worker.c.
Unfortunately, ModWorker is not fully compatible with all Apache modules, including such common ones as ModPHP. Prior to enabling it you should check for compatibility and find alternatives where needed. If you need both ModWorker and PHP, for instance, you can use Mod_FastCGI in place of ModPHP.